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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[November, 



Mr. Wicksteed, and consequently not (o be deppnfled upon; never- 

 theless we cannot but think that a still longer continuance of observa- 

 tions is necessary to confirm the opinion expressed by Mr. Wicksteed, 

 that evaporative economy is promoted by more rapid combustion, as 

 compared to the slow combustion elTected in the Cornish boilers, the 

 rapidity of combustion being measured by the weight of coals burned 

 ou each square foot of grate per hour, for we do not consider it fully 

 borne out even by his own experiments. Nor should we have sup- 

 posed that the amount of heated surface which would produce the 

 maximum of evaporation with a given weight of fuel had been sur- 

 passed, even in the Cornish boilers, which Mr. Wicksteed states to be 

 proved by his experiments. 



With the engines the case is very different: — tlie circumstances 

 which affect the economv of ittarii are simple and manifest, and their 

 effects easily ascertained and measured ; for which reason this part of 

 the investigation is much more satisfactory than the former. But the 

 dulij or effect produced by the engine with the consumption of a given 

 quantity of fuel, resulting from the combination of the evaporative 

 economy of the boiler, and tlie economy of the engine in the expendi- 

 ture of steam, must necessarily be an uncertain criterion of the excel- 

 lence of an engine, unless deduced from observations continued through 

 a considerable length of time, and unless due account be taken at the 

 same time of the various circumstances affecting the evaporative 

 economv of the boilers. For this reason the author has adopted the 

 judicious plan of separating the two sets of causes and effects, by as- 

 cert.iining, for the boilers, the weight of water evaporated per lb. of 

 coals, and for the engines, the weight of water used as steam in the 

 engine to produce the observed effect. By this means he has been 

 enabled to obtain the relative commercial values, if not of the boilers, 

 at least of the engines experimented upon. 



By an inspection of Table No. VII., which contains the particulars 

 of the experiments upon the engines, it will be seen that the duty in- 

 creases progressively with the degree of expansion of the steam in 

 the cylinder ; also that there is very little difference between the mean 

 steam pressure on the piston and the mean resistance, that difference 

 being in favour of the steam pressure, thus proving that there is no 

 necessity whatever to call in the ptrcusnive force of the steam to assist 

 its elastic force in overcoming the resistance, according to the new 

 theory which Mr. Parkes attempted to establish. 



It will be remarked, on examining column 27 of this table, that the 

 mean steam pressure was always found to exceed the mean resistance, 

 and that the excess increased progressively with the degree of ex- 

 pansion : but on this point we have one or two observations to 

 make. 



The mean steam pressure, (column 21), is calculated from the 

 quantity of water in the form of steam used per stroke in the cylinder, 

 (column 9) ; the quantity of steam remaining in the cylinder from the 

 preceding stroke when the steam valve is opened (column 12), de- 

 duced from the pressure of that steam (column 9) ; the space above the 

 piston upon the shutting of the steam valve (column 15), whence is 

 deduced the pressure of the steam before expansion (column 16) ; the 

 proportion of the stroke through which the steam expands, (column 

 2U) ; and the pressure at the end of the stroke (column 17). 



We have to observe with respect to these calculations, that the 

 pressure of the steam is always supposed to be proportional to its 

 density, (except in the case of col, 13, where Trcdgold's rule is used 

 to determine the volume of the steam at boiler pressure generated 

 from the quantity of water used per stroke) which occasions a slight 

 error in each of the columns 12, 14, and Hi ; and in col. 17, an average 

 pressure at the end of the in-door stroke of 6-71b. per square inch is 

 assumed, but which we find by calculation from the quantity of water 

 used per stroke, supposing the pressure in column 11 to be correct, to 

 vary in the five experiments upon the Cornish engine from 8'021b. to 

 6'Oil, diminishing as the degree of expansion increased. After making 

 these corrections, as well as a slight alteration in col. 13, from the use 

 of a different method, we find the mean pressure of steam in the ex- 

 periments B, C, D, E, and F, = 12-581b., 12-301b., 13-UGlb., 13-331b., 

 and 12-8lb., respectively, the mean resistance in all cases being as- 

 sumed to be 12-941b., the power thus appearing to be sometimes 

 superior, and sometimes inferior to the resistance, but never differing 

 from it more than 0-391b., per square inch, which may almost be con- 

 sidered as a practical equality. 



In the experiment H, on the Boulton and Watt engine, the excess of 

 the steam ))ressure over the resistance becomes greater after the cor- 

 rections ; but that is evidently to be accounted for by the quantity of 

 water used per stroke being estimated too highly, fur we find the 

 pressure at the end of the stroke 12-S31b., (instead of lU-25lb., as given 

 in the table both for this pressure and that of the steam remaining in 

 the cylinder before the steam valve is opened), which is no doubt 

 erroneous. At all events these experiments sutficiently prove the 



capability of the Cornish engine to perform the duty it is asserted 

 to do. 



We regret that we cannot give a few more extracts from this 

 valuable work, which contains several tables that deserve the attentive 

 perusal of all parties in any way connected with the steam engine, 

 particularly in a commerckd point of view. To Mr. Wicksteed the 

 public are greatly indebted for his indefatigable exertions and perse- 

 verance in carrying out his experiments, and laying the facts open to 

 all without the sliglitest concealment or mystery. 



Lardtier'i Cabinet Cyclopadia — Treatise on Ehctricily, Magnetism, IfC. 

 Bv Dionvsius Lardner, LL.D. Vol. I. London: Longman & Co. 

 1S41. 



The Cabinet Cyclopsedia has now reached its 130th volume, a su6B- 

 cient proof of its popularity and its consequent utility. In the present 

 work Dr. Lardner discusses electricity, magnetism, electro-chemistry, 

 electro-magnetism, terrestial magnetism, v'v.'c, subjects all of the high- 

 est interest, and of the greatest importance to the votaries of science 

 and to practical men. The progress of these sciences is most rajiid, 

 every day new powers are developed, and new and extraordinary 

 applications are carried into effect. The mere experimental history 

 of electricity is important as shadowing out the future, were not the 

 results already produced sufficient to stamp its value. Under such 

 circumstances the necessity for a popular digest of the scattered in- 

 formation on electricity is imperative, and also that it should be exe- 

 cuted by one who has proved himself competent for the task. In the 

 next volume Dr. Lardner proposes to conclude the treatise, to record 

 the latest discoveries, and describe the several practical applications. 

 We are glad to see the severity with which the Doctor handles M. 

 Arago for trying to supplant Franklin by a French intruder, as he sub- 

 sequently attempted to do with regard to Watt, when he received 

 merited castigation at our hands. 



Vitn of the Oiise I'alley F'iaducl on the London and Brighton Railway. 



London: Ackerman & Co. 1841. 



The great progress of those magnificent public works, the railways, 

 has led to the publication of numerous engravings devoted to their 

 illustration. Messrs. Ackerman, who are so successful in the pretty, 

 seem determined to show their capability for the grand, and they 

 could scarcely have chosen a better subject than Mr. Rastrick's Ouse 

 Valley Viaduct.'which steps across the Lowlands with 37 arches of 

 30 feet span, the highest standing a hundred feet above the water. 



Elements of Perspective Draning. By Augustus Deacon. London : Tay- 

 lor and Walton. 1841. 



This work, the designs only of which are by Mr. Deacon, but the 

 plan of which emanates from a well-known promoter of this branch of 

 education, is calculated to be highly useful to the student of mechani- 

 cal drawing. The author grounds his system on the use of a series of 

 models, to which, however we should object in some cases, as being 

 too small ; some system, however, is better than the present want of 

 system. 



A Letter to the Shareholders of the Bristol and Exeter Railway. By 

 W. Gravatt, C.E., F.R.S. London: M'Dowall. 18U. 

 We really do not see that we can with propriety enter into the 

 subject matter of this pamphlet, for there has been already so much 

 unpleasant discussion and recrimination, that we are most unwilling 

 to have our columns occupied witli a subject so painful, which the 

 farther it is debated, the more productive of ill-feeling does it 

 become. 



Outline of a system of Model Mapping. By J. Bailey Denton, Sur- 

 veyor, Gray's Inn Square. London, Weale, 1811. 

 Mr. Denton's chief object in producing this pamphlet, has been to 

 call the attention of the agricultural interests to the superiority of 

 model mapping as a means of delineation, and to its application as a 

 basis for draining and irrigating operations. The author shows for- 

 cibly the advantages to be derived not only from a proper collectioa 



